1. Field of the Invention
The present invention relates to the manufacturing method of an electron-emitting device, and more particularly, to electron sources, display panels, and image forming apparatuses, employing the aforementioned electron image device.
2. Related Background Art
Conventionally, two types of electron emission devices have been known; i.e., thermionic type and cold cathode type. Types of cold cathode electron-emitting devices include; field emission type devices (hereafter referred to as “FE type device”), metal/insulator/metal type devices (hereafter referred to as “MIM device”), surface conduction electron-emitting devices (hereafter referred to as “SCE device”), etc.
Known examples of reports of FE type devices include: W. P. Dyke & W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89(1956); and “Physical properties of thin-film field emission cathodes with molybdenum cones”, J. Appl. Phys., 47, 5248(1976); etc. Known examples of reports of MIM devices include: C. A. Mead, “The tunnel-emission amplifier” A. Appl. Phys., 32. 646(1961); etc. Known examples of reports of SCE type devices include: M. I. Elinson, Radio Eng. Electron Phys., 10, (1965); etc.
The SCE device takes advantage of the phenomena where electron emission occurs when an electric current is caused to flow parallel to a thin film, this thin film of a small area being formed upon a substrate. As for examples of such surface conduction electron-emitting devices, in addition to the device by the aforementioned Elinson et al using SnO2 thin film, there have been reported those which use Au thin film [G. Dittmer: “Thin Solid Films”, 9,317(1972)], In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad: “IEEE Trans. ED Conf.”, 519(1975)], and carbon thin film [Hisashi Araki et al: Shinku, Volume 26, No. 1, page 22 (1983)], etc.
FIG. 18 illustrates the construction of the aforementioned Hartwell device as a classical example of such a surface conduction electron-emitting device. In this Figure, the numeral 1 denotes a substrate. The numeral 4 denotes an electroconductive film formed by sputtering in an H-shaped form of metal oxide thin film, etc., and the electron-emitting region 5 is formed by a later-mentioned current conduction treatment called energization forming. In this Figure, the spacing L between the device electrodes is set to be 0.5 to 1 mm, and the device width W′ is set at approximately 0.1 mm. The form of the electron-emitting region 5 has been illustrated in a type drawing.
Conventionally, with these surface conduction electron-emitting devices, it has been common to form the electron-emitting region 5 by conducting a current conduction treatment called energization forming on the electroconductive film 4 beforehand; i.e., energization forming refers to the process of applying either a direct current or an extremely slow rising voltage, such as around 1V/minute, to both edges of the electroconductive film 4 so as to cause local destruction, deformation, or deterioration, thereby forming an electron-emitting region 5 having high electrical resistance. Further, regarding the electron-emitting region 5, a fissure has formed at one portion of the electroconductive film 4, and electron emission occurs from the proximity of this fissure. The member which has been subjected to local destruction, deformation, or deterioration, by means of energization forming upon the conductive film is referred to as the electron-emitting region 5, and the conductive film 4 upon which the electron-emitting region 5 has been formed by means of energization forming is referred to as the electroconductive film 4 which contains the electron-emitting region 5. The aforementioned surface conduction electron-emitting device which has been subjected to energization forming one where voltage is applied to the electroconductive film 4 which contains the electron-emitting region 5, and electrical current is caused to flow through the aforementioned device, thereby causing emission of electrons from the electron-emitting region 5.
Further, the aforementioned surface conduction electron-emitting device has the advantage of enabling arrayed formation of a great number of devices over a wide area, due to the construction thereof being simple and the manufacturing thereof being relatively easy. Accordingly, many applications for employing this advantage have been researched, a few examples being charged beam source and display apparatuses. An example of a great number of surface conduction electron-emitting devices being arrayed is the electron source of the so-called ladder-type device, wherein, as described later, both edges of individual surface conduction electron-emitting devices arrayed in a parallel manner are wired together by means of wiring (common wiring) so as to create a row, and many such rows being arrayed (e.g. Japanese Patent Laid-Open Application No. 1-031332, Japanese Patent Laid-Open Application No. 1-283749, Japanese Patent Laid-Open Application No. 2-257552, etc.). Also, while in recent years image forming apparatuses such as display apparatuses which are flat-type display apparatuses employing liquid crystal have become commonplace in the stead of CRT apparatuses, such flat-type display apparatuses employing liquid crystal have problems such as requiring back lightning due to not being emission type, and development of an emission type display apparatus has been awaited. An example which can be given of an emission type display apparatus is an image-forming apparatus with a display panel which is comprised of an electron source of many arrayed surface conduction electron-emitting devices, and fluorescent substance which is caused to emit visible light by means of the electrons emitted from the electron source (e.g. U.S. Pat. 5,066,883).
The known method employed for the manufacturing of electron-emitting devices such as described above has been a photo-lithographic process according to known semiconductor processes.
While the aforementioned surface conduction electron-emitting device can be applied to image-forming apparatuses and other such apparatuses by means of creating and arraying a great number of such surface conduction electron-emitting devices upon a substrate with a wide area, such an arrangement manufactured with known photo-lithographic processes would result in extremely high costs. Accordingly, it has been necessary to employ a manufacturing method with lower costs. To this end, a method has been suggested as a method for forming such devices on a substrate with a wide area, wherein printing technology is employed for forming the electrodes 2 and 3, and formation of the electron-emitting film 4 is conducted by employing an ink-jet method in which droplets of a solvent containing organic metal compounds are deposited onto the substrate in a partial manner (e.g., Japanese Patent Application No. 6-313439 and Japanese Patent Application No. 6-313440).
Now, description of an overview of the manufacturing process for electron-emitting devices employing printing technology and ink-jet method will be given with reference to FIGS. 3A through 3E.    1) An insulating substrate 1 is thoroughly washed with detergent, pure water, and organic solvent, following which device electrodes 2 and 3 are formed upon the surface of the aforementioned insulating substrate 1, employing screen printing technology or offset printing technology (FIG. 3A).    2) Droplets of a solution containing such as organic metal compounds, for example, are deposited at the gap portion of the device electrodes 2 and 3 on the insulating substrate, employing droplet-depositing means, so that the deposited droplets connect both electrodes upon which they are deposited. This substrate is dried and baked, so as to form the electroconductive thin film 4 for forming the electrode-emitting region (FIG. 3D).
However, depositing droplets upon the printed electrodes employing an ink-jet method results in problems such as follows; i.e., in an event where the density of the printed electrode is low, a phenomena may occur where the deposited droplets penetrate into the electrode by capillary action. This causes the amount and spread of the liquid to be irregular at the gap portion, causing irregularities in the thickness of the electroconductive film after baking, irregularity in film thickness from one device to another, and irregularities in electric properties.
Also, while this is not a problem confined to the ink-jet method, in the event that the surface conditions of the substrate are not uniform or the wettability of printed electrodes and the substrate are not the same, the droplets are repelled, making formation of a uniform film to be difficult.
Further, when employing the ink-jet method to formation of a later-described large-area display apparatus, it becomes necessary to deposit a great number of droplets upon the substrate in order to form a great number of electroconductive films. Accordingly, the amount of time elapsed following depositing of the droplets upon the substrate, during which time the deposited droplets are left to stand, differs between each of the electroconductive films. Consequently, the organic metal compounds contained within the droplets crystallize, which may cause non-conformity in post-baking film thickness of the electroconductive films and irregularity in the resistance of each of the electroconductive films corresponding to each of the devices.
Moreover, as described in Japanese Patent Laid-Open Application No. 1-200532, regarding manufacturing methods of electron-emitting devices, in order to obtain electroconductive film comprising fine particles of metals or metal oxides to which energization forming processing can be applied, a process has been conducted wherein a thin film of an organic metal compound such as palladium acetate is formed between the device electrodes, following which a baking process referred to as baking is applied to the electroconductive thin film. This known baking process is conducted in order to form a thin film from fine particles of metal or metal oxide due to heat decomposition of the organic metal compound in an atmosphere of air, etc. The heat processing temperature of this known method has been a temperature higher than the melting point or the decomposition point of the organic metal compound.
As a result of the known process, wherein the electroconductive thin film of the organic metal compound is heated to a temperature higher than the melting point or the decomposition point thereof in order to obtain an electroconductive film before conducting energization forming, part of the metal contained within the organic metal compound is lost either to volatilization or sublimation, resulting on thinning of the thickness of the obtained thin film of fine particles of metal or metal oxide, and further creating a problematic situation wherein precise control of the film thickness is difficult.
Further yet, in the event where non-volatile organic compounds are employed for formation of the electroconductive film, crystal precipitation and deformation of the droplets occur during the drying process, making for irregularities in the film thickness, again resulting in a problem wherein precise control of the film thickness is difficult.
Moreover, in the manufacturing process of image-forming apparatuses wherein multiple electron-emitting devices are arrayed, difference in the thickness of the formed electron-emitting devices arises owing to the fact that there is difference in the time from when droplets are deposited on each device till the baking process.
Consequently, in surface conduction electron-emitting devices manufactured according to the aforementioned method, there is great irregularity in the thickness of the electroconductive films and electric properties such as sheet resistance value, thereby resulting in occurrence of brightness irregularities and defective products in resultant electron sources, display panels, and image-forming apparatuses, using the electron-emitting devices.